Field of the Invention
The present invention relates to a distortion aberration correction mechanism for correcting distortion aberration due to an imaging optical system by performing image processing. Further, the present invention relates to an image processing apparatus including a blurring correction mechanism for correcting a blur of an image formed on an image sensor due to a movement of an imaging apparatus.
Description of the Related Art
Japanese Patent Application Laid-Open No. 2005-252626 discusses an image processing apparatus including the following functions. The image processing apparatus includes a function for correcting distortion aberration unique to an imaging optical system by performing image processing. Further, the image processing apparatus includes a blurring correction function, i.e., an electronic image stabilization function, capable of correcting a blur of an object image caused by a movement of the imaging apparatus when capturing an image.
When image processing for reducing the distortion aberration is performed on an image in which the distortion aberration unique to the imaging optical system has occurred, a wide-angle distortion occurs in the image. The wide-angle distortion occurring in the image of a planar object is unnoticeable. However, the wide-angle distortion occurring in the image of a solid object is noticeable. In particular, when the image is captured by setting an image angle of the imaging optical system including a zoom function to a wide angle, a large amount of distortion aberration occurs in the image. Therefore, the wide-angle distortion, which occurs when the distortion aberration is corrected, also becomes large.
When the wide-angle distortion occurs, the object in a peripheral portion of a screen is stretched in an image height direction of the screen. In such a case, the image causes a strong feeling of strangeness to a user particularly when the wide-angle distortion occurs with respect to a face of a person.
FIG. 7A is a schematic diagram illustrating an image in which the distortion aberration has been well corrected. As illustrated in FIG. 7A, planar shapes formed on linear lines appear to be normal. However, the wide-angle distortion tends to occur on the solid object, such as the face of the person, in the peripheral portion of the screen, so that the image causes a feeling of strangeness to the user. FIG. 7B is a schematic diagram illustrating an image in which a barrel-type distortion aberration remains. As illustrated in FIG. 7B, the planar shapes formed on the linear lines are distorted, so that the image causes a feeling of strangeness to the user. However, the solid object, such as the face of the person, in the peripheral portion of the screen appears to be relatively normal in the image. Therefore, when a large amount of distortion aberration has occurred, the image with comparatively satisfactory planar shapes formed on the linear lines as well as comparatively satisfactory wide-angle distortion can be obtained by the correction leaving a small amount of distortion.
On the other hand, an electronic image stabilization processing, as image stabilization processing, reduces a blur of an image caused by the shake of the imaging apparatus. The electronic image stabilization processing shifts a clipping area to be actually output (i.e., recorded or displayed) from the image according to the shake of the imaging apparatus, and thus reduces the blur of the image.
However, if there is distortion aberration left in the image generated by using the output from the image sensor when a moving image is captured, a state of the distortion aberration included in a clipped image changes according to a change in a position of the clipping area to be actually output. FIGS. 8A, 8B, and 8C are schematic diagrams illustrating changes in the state of the distortion aberration left in each clipping area according to the change in the position of the clipping area. More specifically, FIGS. 8B and 8C illustrate the images generated from the image illustrated in FIG. 8A by changing the clipping positions. The states of the distortion aberrations left in the respective images illustrated in FIGS. 8B and 8C are thus different. As a result, the difference in the distortion aberrations left in the images becomes noticeable due to the change in the clipping positions in the moving image in which such images continue.
Further, if brightness of the object is low, a combining method may be performed as follows. Imaging is performed a plurality of times to obtain a plurality of image data, and the same object is detected from each of the obtained plurality of the image data. The positions of the plurality of the image data are then adjusted so that positions of the same object included in each of the plurality of the image data match each other, and the plurality of the image data is combined.
In such a case, if the position of the same object on the image sensor is different among the plurality of images, the state of distortion aberration left in the object also becomes different among the plurality of images. FIGS. 9A, 9B, 9C, and 9D are diagrams illustrating the change among the plurality of images in the state of distortion aberration left in each image, which has been clipped according to the object, caused by a shift in the position of the object on the image sensor. More specifically, FIGS. 9B and 9C illustrate the images in which the clipping positions are different, generated from the image illustrated in FIG. 9A. In such a case, the state of the distortion aberration left in each image is different. Therefore, if such images are combined, the image in which differently-shaped object images are combined is generated even when the object is the same. As a result, the object becomes blurred in the image.